Method of treating magnetic materials



Patented Jan. 5, 1932 UNITED STATES PATENT orr cs KENNETH LOYAL soon, or wEsTENN srnrNos, ILLINOIS, ASSIG-N'OR To wnsTmN nnnornrc comm, INCORPORATED, or EW Yonx, N. m, a coRromTIoN or NEW, YORK wanton or TnnATme memo mTEmaLs Application filed November 8, 1927. Serial No. 231,924. J

This invention relates to a method of treatiarly to a method of heat treating m gnet 5: An object of the invention is to pro ide a method for improving the magnetic properties of magnet steel.

In accordance with the general features of the invention, the ma ent steel, such as oobalt or tungsten steel is first brought to approximately its maximum magnetic hardness at which point it would, after being magnetized to saturation, have a certain residual induction. The steel is then tempered to an intermediate degree of hardness which cannot be obtained directly, after which it'will, after being magnetized to saturation, have an increased residual induction. By magnetic hardness is meant that quality of a magnetic material which causes it to resist magnetization and demagnetization. In a given material, it is proportional to the coercive force but is not proportional to the residual induction as will appear more fully below.

ing of the invention may be had by reference to the following description taken in conjunction with the accompanying drawings, in

whic V I Fig. 1 is a graphic representation of phe- 7 nomena encountered in the hardening of cobalt steel;

Fig. 2 represents hysteresis loops of cobalt steel showing its magnetic properties in the hardened and tempered states, and 1 -Fig. 3 is a graphic representation of the prpperties of cobalt steel upon hardening and tempering.

The invention will be described in connec-. tion with cobalt steel although other steels such as tungsten steel respond to the same method of treatment. The hardening of cobalt steel is accomplished byheat-ing the steel to a temperature of about 17 00 F. or slightly above the A transformation point and thenquenching the steel in oil, water or other suit I ,able quenching medium. It has been found that in heat treating the cobalt steel by raising its temperature to acertain value and then quenching there is no marked increase in the ing magnetic materials, and more pafirticu practically vertical for a considerable dis- It is believed that a complete understandcate flux densities in maxwells per square magnetic hardness of the steel until the temperature is brought to a value between 1600. F. and 1700 E, which is above the A 'ti'ans' formation point before quenching. This is shown graphically in Fig. 1 in which the ab-' scissas represent the temperature in do we Fahrenheit to which a specimen has en raised before quenching, and the ordinates represent the magnetic coercive force in gilberts per ce timeter necessary to bring a specimen whi h has been magnetized to saturation back to zero magnetization. Since the coercive forcevaries with ma etic hardness, the curve in Fig. 1 may e taken to represent the variations in magnetic hardness in specimens of steel which are raised to the different values of temperature shown by the abscissas and then quenched.

It willbe noted that the curve in Fig. 1 is tance indicating. that diflerent degrees of magnetic hardness may be obtained at a single temperature value. The particular magnetic hardness obtained at this temperature is theoretically indeterminate and may be ascertained only by test.-

In experimenting with the heat treatment of cobalt steel it was discovered that if a specimen of the steel is first brought to its maximum magnetic hardness, its residual induction after magnetization to saturation may be greatly increased by subsequently tempering it to a lower magnetic hardness, in which tempering process any desired degree of magnetic hardness may be obtained by reheating the steel to an appropriate temperature.

The improvement in'the residual induction of a specimen of cobalt steel upon tempering it to a lower degree of magnetic hardness after hardening to its maximum extent is shown graphically in Fig. 2 in which the abscissas indicate magnetizing forces-in gilberts per centimeter and the ordinates indicentimeter. The curve 5 represents a hys-' teresis loop. of a specimen. of cobalt steel brought to its maximum hardness and the curve G'represents a hysteresis loop of a temperedispecimen. It will be noted that the residual induction of the tempered specimen, indicated by the point where the loop 6 intersects the vertical axis, is considerably higher than the residual induction of the specimen at its maximum hardness, indicated by the point where the loop 5 intersects the vertical axis. Incidentally it may be observed that while the magnetizing force nec essary to reduce the flux density to zero after the specimens have been magnetized is less in the tempered specimen than in the speci-. men which was brought to its maximum hardness, as long as the coercive force is not reduced below a certain limiting value, which will depend upon the dimensions of the magnets to be made from the steel,'-this fact is of little consequence.

In Fig. 3, in which the abscissas indicate magnetizing forces in gilberts per centimeter and the ordinates indicate remanence in maxwells per square centimeter, the curve 7 represents the magnetic remanence of permanent magnets, guch as bars or horseshoes, brought to various degrees of magnetic hardness and the curve 8 represents the magnetic remanence of similar magnets tempered to various degrees of hardness from their maximum values, showing a maximum magnetic remanence at an intermediate degree of magnetic hardness of the metal between maximum hardness and minimum hardnessin the tempered specimen.

In a specificapplication of the method oi improving the magnetic properties of steel, a magnet containing approximately 36% of cobalt is heated to a temperature of 1700 F. and quenched in oil or water, bringingit to substantially its maximum hardness; The magnet is then reheated to a temperature not to exceed 1300 F. and quenched in airtempering it to a lesser degree of magnetic hardness, increasing the residual induction of the material, and thereby increasing the mag-- netic remanence of the magnet.

It will be understood that the embodiment of the invention herein described and illustrated is merely a convenient and useful formof the invention which is capable of many other modifications without departing from the spirit and scope of the invention.

What is claimed is z 1. A method of improving the magnetic roperties of magnet steel containing 5% to 0% cobalt, which comprises heating the steel .to a temperature adapted to produce a high'giegree of magnetic hardening, quenching the steel, reheating'to a lower temperature adapted to produce an intermediatedegree of magnetic hardening, and quenching the steel. Y

f2. A method of improving the magnetic properties of steel containing 5% to 60% cobalt, which comprises heating the steel to a temperature of. approximately 17 00 F., quenching the steel, reheating the steel to a quenching the steel.

temperature not to exceed 1300 F., and

a temperature adapted to produce a high degree of magnetic hardening, quenching the steel rapidly, reheating to a lower temperature adapted to produce an intermediate de-' gree of magnetic hardening, and quenching the steel slowly. I

i. The method of improving the magnetic properties of cobalt magnet steel, which comprises rapidly quenching the steel from a temperature of approximately 1f700 to produce a high degree of magnetic hardening, and subsequently quenching the steel from a temperature not exceeding 1300 F. to produce an intermediate degree of magnetic hardening.

5; A method of improving the magnetic properties of cobalt magnet steel, which comprises heating the steel to a temperature adapted to produce a high degree of magnetic hardening, quenching the steel, reheating the steel to a temperature adapted to produce an intermediate degree of magnetic hardening, and slowly cooling the steel.

6. The method of improving the magnetic properties of cobalt magnet steel, which comprises bring it substantially to its maximum magnetic hardness, and subsequently reheating and slowly cooling the steel to produce a lesser degree ,of magnetic hardness whereby its -magnetic remanence is increased.

7 The-method of improving the magnetic properties of steel containing 36% cobalt, which comprises rapidly quenching the steel from a temperature of approximately 17 00 F. to produce a high degree of magnetic hardening, and subsequently quenching the steel from a temperature not exceeding 1300 F. to produce an intermediate degree of magnetic hardening.

8. A method of improving the magnetic heating and quenching the steel to I properties of steel containing 36% cobalt,

which comprises heating the steel to a temperature adapted to pro uce a high degree of magnetic hardening, quenching the steel, reheating the steel to a temperature adapted to produce an intermediate degree of magnetic hardening, and slowly cooling the steel.

9. The method of improving the magnetic properties of magnet steel containing 36% cobalt, which comprises heating and quenching the steel to bring it substantially to its maximum magnetic hardness, reheating and slowly cooling the steel to produce 'a lesser degree of magnetic hardness whereby its magnetic remanence is increased.

10. The method of improving the magnetic properties of cobalt steel, which comprises heating the steel to a temperature above its A transformation point, then quickly cooling the steel, then reheating the steel "to a, temperature adapted to produce an intermediate degree of magnetic hardening but not above 1300-F., and then 'cooling the steel.

In Witness whereof, I -hereunto subscribe my name this 25th day of October A. 1)., 1927 KENNETH ILOYAL SCOTT. 

